Pressure and temperature sensors are utilized in a variety of commercial, consumer and industrial applications. Pressure and temperature transducers are well-know sensing devices. One type of pressure transducer, for example, is a device formed with a silicon substrate and an epitaxial layer, which is grown on the substrate. A portion of the substrate can then be removed, leaving a thin, flexible diaphragm portion. Sensing components can be located in the diaphragm portion to form a pressure transducer. In operation, at least one surface of the diaphragm can be exposed to a process pressure.
In a pressure and/or temperature pressure-sensing configuration, a diaphragm deflects according to the magnitude of the pressure, and this deflection bends the attached sensing components. Bending of the diaphragm creates a change in the resistance value of the sensing components, which can be reflected as a change in the output voltage signal of a resistive bridge formed at least partially by the sensing components.
Some techniques for forming a composite diaphragm for a pressure transducer or similar device involve configuring a substrate layer having a first conductivity type, wherein the substrate layer includes a first surface. Positive implants can then be deposited in the first surface of the substrate layer, and an epitaxial layer grown on the first surface of the substrate layer so that the positive implants form positive diffusions in the epitaxial layer. An oxide pattern can be then formed on the epitaxial layer, and a top layer deposited over the epitaxial layer and oxide pattern. The substrate layer and positive diffusions of the epitaxial layer can then be etched to form the composite diaphragm. Such a composite diaphragm can therefore be provided for use in a pressure sensor or like device. The diaphragm comprises a first layer of silicon nitride and a second layer attached to the silicon nitride layer and comprising a pressure sensor pattern of silicon material.
Pressure transducers of the type which comprise a thin, relatively flexible diaphragm portion of suitable material, such as silicon or ceramic, on which either a selected resistive element or a capacitive plate is printed whereby exposure to a pressure source causes deflection of the diaphragm will cause a change in the resistive value of the resistive element or a change in the spacing of the capacitive plate with a mating capacitive plate and concomitantly a change in capacitance are therefore well known in the art.
When used as a low-pressure sensor, for example, economical packaging of the transducer in a housing so that an effective seal is obtained while at the same time preventing stress related to the mounting and sealing of the transducer from influencing the output becomes problematic. This is caused, at least in part, by the significant difference in thermal expansion between the material used to form the transducer, e.g., silicon, ceramic or the like, and the housing of plastic or the like.
A conventional sealing arrangement involves placement of a ring of sealing material around an inlet pressure port in a housing and mounting the transducer so that the pressure sensitive diaphragm is precisely aligned with the pressure port. This conventional arrangement not only involves stress isolation issues, it also limits flexibility in design choices in defining the location of the transducer within the package.
Typical sensors utilized to measure both temperature and pressure simultaneously are limited by the manner in which the pressure sensing technology utilized is attached to the pressure connection or port. An internal seal or gasket is typically utilized to seal the connection, but such components limit the burst pressure of the sensor to approximately three to five times the operating range.
Another difficulty cause by these types of sensors is that varying seal materials are required to accommodate a wide range of sensing media. In other words, the sensor's mechanical structure must be matched to the media present in the measurement. Additionally, typical solutions offer few options for pressure and/or temperature range, usually limited to one or two options. For example, such sensors usually offer only one output type for pressure and temperatures and one type of electrical termination. Such devices offer few ports for pressure and/or temperature connections. If something other than these standard options is desired, then a special sensor must be constructing, adding time and costs to the construction of the sensor.
Based on the foregoing it is believed that what is need to overcome the aforementioned problems is the development of an improved pressure and temperature sensing device that allows a number of varying options without requiring special sensor configurations, while accommodating a wide range of sensing media.